1. Field of the Invention
The present invention relates to a direct injection type internal combustion engine.
2. Description of the Related Art
In a known direct injection type engine, when the engine is operating under a light load, an air-fuel mixture is formed in a restricted region in the combustion chamber, the remainder of the combustion chamber is filled with air, and the air-fuel mixture is ignited by the spark plug. Conversely, when the engine is operating under a middle load or under a high load, the entire interior of the combustion chamber is filled with an air-fuel mixture (U.S. Pat. No. 4,955,339)
Usually, an engine has a construction such that a fuel vapor produced in, for example, the fuel tank, is purged into the intake passage of the engine, and to this end, the engine is normally provided with a purge control device. When, however, the air-fuel mixture is burned in the presence of excess air when the engine is operating under a light load, as in the above-mentioned direct injection type engine, if the fuel vapor is purged into the intake passage of the engine when the engine is operating under a light load, the fuel vapor spreads in the air in the combustion chamber, and thus a large part of the fuel vapor is discharged into the exhaust passage of the engine without being burned. Nevertheless, in such an engine, a catalytic converter for purifying the exhaust gas is normally arranged in the exhaust passage of the engine, and therefore, even if a large part of the fuel vapor is discharged into the exhaust passage without being burned, as mentioned above, the fuel vapor is oxidized, i.e., purified, in the catalytic converter, and there is no danger of a harmful gas being discharged into the outside air.
Nevertheless, the oxidizing of the fuel vapor by the catalyzer, i.e., the exhaust gas purifying operation, cannot be properly carried out until the temperature of the catalyzer in the catalytic converter rises to a given temperature, i.e., until the catalyzer is activated. Accordingly, when the temperature of the catalyzer is lower than the tolerable minimum temperature at which the fuel vapor can be sufficiently oxidized, i.e., at which the exhaust gas can be sufficiently purified, if the fuel vapor is discharged into the exhaust passage, a problem occurs in that the fuel vapor is discharged into the outside air without being fully oxidized, i.e., a harmful gas is discharged into the outside air.